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Colours – Part 03 (more light on colours)

Since last two posts, we have established a good tempo and talking about Colours! Right? Yesterday, I was compiling all the notes for this post and was sorting topics. And while doing that, I was sort of thinking to ask my doubts to some one who can answer me well. While thinking about that I started dreaming of a meeting with such a one. I immediately called him and asked for his appointment and to my surprise he agreed. And you know what? Today, We have that very spacial guest with us.

‘Mr. Light’ himself. Yes The Great Mr. LIGHT HIMSELF! Ta Da!

Me: Hello Sir!

Mr. L: Hi Mahesh, how are you?

Me: I’m Great! Its my pleasure to see you. And how do you do, sir!

Mr. L: Pretty straightforward. But Mahesh, I am afraid that I have very short time for discussion now. I have to go to my friends birthday. Her name is twinkle. In next 15 seconds I have to reach there. So ask it quickly.

Me: OK, OK. Sir. I will ask you as fast as possible! I was discussing with my friends about how do we ‘see’. Can you describe us, how do we humans see colours? We would love if, you will put some light on that.

Mr. L: OK Time’s up. I need to go now. I will talk with you later! Till then why don’t you google about that your self? Hmm?

And suddenly a big flash of light crossed over my head and then…

…and then nothing. I just woke up.

OK, OK, don’t through that mouse towards me. I was just kidding. Sorry! 😀

Let’s come to our main discussion and this time no rubbish kidding!

“Light is a kind of Electro- Magnetic Radiation (EMR)”.

Which means that, while traveling ‘straightforward’ it actually moves like this:

Yes! It actually flows in such a wavy pattern, over and over. Each Electro-magnetic particle has a ‘charge’ in it, which lets it oscillate in a particular way. As shown in the picture, the distance between each wave is called its ‘wavelength’. And this wavelength plays a great role in our lives.

One of a very common type of EMR is the Radio-wave. It can have a wavelength of about the height of Eiffel tower or even up to 1km. Or in other words, those waves having this much long wavelengths are called radio-waves. When wavelength is about the size of your mobile phone (10 to 15 cm), we call it a ‘Radar’ wave. When it is still shorter, say about 1mm, it is called ‘microwave’. And what if the wavelength is still smaller? If it is as small as a needle point, we call it the ‘Infra-Red’. Which is from 1mm to 750 nm (nano meters). Bye the way one millimetre means 10,00,000 nano meters. And what if the wavelength is still decreased?

I know what you are thinking, “Hay Mahesh! What’s going on? Are you still kidding? Aren’t we supposed to discuss about colours? Where are the colours? eeemm?”

But wait amigos! We are very near to the colours now! If the wavelength of a wave is smaller than 750 nm then we can actually ‘see’ it. Yes! That is what we call as light. Our ‘Mr. Light’. Visible light’s waves can be as small as 390 nm. Human eyes can see such light, between 750 nm to 390 nm. This range of wavelengths is nothing but the ‘COLOURS’. The VIBGYOR! Yes, it is really like that. Very surprised, right?

The ‘R’- the Red, in the VIBGYOR spectrum, means particles having wavelength smaller than 750nm. Orange is about 620nm. Yellow is even smaller than 590. Green is between 570 to 495nm. Blue is about 480 nm. Indigo is even shorter wavelength. And the ‘V’ for violet means wavelength between 450nm to 380nm. So the entire colour range that we can see is between 750 to 390nm.

If we keep on reducing the wavelengths of the EMR we get Ultraviolet between 390 up to just 10 nm. Further on, we get X-rays and Gamma rays. But we can not see any of them. So our colour system is only ‘relative’ to this visible colour spectrum. Between Infra-red to Ultraviolet. Other animals, birds or fishes etc. may have some property in there eyes that can ‘see’ those other wavelengths. There may be an animal having X-Ray vision or infra red vision.

We do see colours because of some spacial cells present in our retina (the inner back surface of our eye ball). The retina contains two important types of cells which actually receives these wavelengths. One type of cell is called the ‘Cone’ cells. They work as the receptors of colours. Due to these cells we see colours. These cells gives signal to brain, when hit by various wavelengths of particles. The other cell type is called the ‘Rod’ cells. These type of cells mainly work to detect the illumination level. Means brightness or darkness of the light is detected by these cells. Which is typically called the Gray-scale value. The cone cells also have three distinct sub types. Each are sensitive to some types of colours only. To keep it simple we can say, first type is sensitive to RED colour, second is to green, and the third is to bluish.

Today, we talked about Light, Electro- Magnetic radiation, colour spectrum and also about Rod and cone cells. In the next post, we will go further and see what are primary colours, mixing of colours etc. If you have missed the earlier discussions by chance, here is the link for first post and second post. So stay tuned. Please give your comments and feed-back. See you next time, Bye Bye!